一株快速转化甜菊苷的细菌鉴定、产酶及转化特性

Identification, culture Optimization and Biotransformation of a Stevioside-degrading Bacterium

摘要:

摘要：【目的】本研究旨在鉴定了一株筛选的甜菊苷特异降解菌、优化了该菌产β-葡萄糖苷酶的条件以及研究了该菌对甜菊苷的转化特性。【方法】经16S rRNA基因序列测序和系统发育学分析，结合形态学特征确定该菌株的系统发育地位。用单因素及多因素分析探讨了其对甜菊苷的降解，通过液质联用检测了降解产物。【结果】菌株-J2与巨大芽孢杆菌的16S rRNA基因序列相似性达到100%，结合形态学特征，鉴定该菌为巨大芽孢杆菌(Bacillus megaterium)。在玉米淀粉4%、豆粕粉1%、硫酸镁0.04%、pH 7.0

Abstract:

Abstract: [Objective] Our study aimed at screening and identifying a specific bacterium capable of degrading stevioside. We also studied the conditions of enzyme production and stevioside conversion. [Methods] Taxonomic group of the strain was confirmed by physical characterization and phylogenetic analysis by 16S rRNA gene sequence analysis and phylogenetic tree construction of the strain. The optimum conditions of enzyme producing and stevioside degrading were studied by single factor and multi-factor statistical analysis. Degradation product was detected and identified via liquid chromatography-mass spectrometry. [Results] Based on the result of 16S rRNA gene sequence analysis, the strain named J2 shares 100% sequence identity with the sequence of the Bacillus megaterium. The activity of beta-Glucosidase produced by this Bacillus megaterium strain was up to 779.68 U/ml with 4% maize starch, 1% defatted soybean, 0.04% MgSO4 and 0.2% stevioside as culture medium when fermented under the condition of pH 7.0, 37℃, 220 r/min and 10% inoculum for 36 h. The results of conversion showed that 10 mg/ml stevioside can be converted to steviolbioside by 74% after 3 days which has been identified by LC-MS. The ratio of rebaudioside A and stevioside was increased to 0.99 compared to original solution 0.38, which lead to 160.5% increasement of rebaudioside A in the relative amount. Stevioside can be converted completely after 5 days. [Conclusion] The isolated strain J2 was identified as Bacillus megaterium. It was a novel and safe strain with high, specific conversion stevioside to steviolbioside ability.